Typically Geared Rotary Actuators can be used to move leading edge flaps of aircraft wing structures in order to alter the lift characteristics of the wing. Conventionally each actuator includes an epicyclic-type reduction gear train which transmits rotation of an input member to a pair of output members one of which is affixed to the wing structure, and so is usually referred to as an “earth” and the other of which is coupled to the control surface to move the control surface relative to the remainder of the wing structure. Moreover, it is conventional to mount two or more actuators in axial, side-by-side relationship with their input members interconnected so as to rotate in unison, and the earths of adjacent actuator “slices” defined by a single component secured to the wing structure in use, the integral earth structure serving both adjacent actuator “slices.” In such an arrangement it is conventional to refer to the whole construction as a geared rotary actuator and to refer to the individual input, gear train, and output assemblies as “slices” of the actuator.
An arrangement of the kind described above is illustrated in our European Patent 0174820. In European Patent 0174820 three actuator slices, 10, 11, and 12 are mounting an axial alignment, and the slices 10 and 11 share a common earth component 17 while the slices 11 and 12 share a similar common earth component connected by a mounting bar 31 to the earth component 17.
European Patent 0174820 discloses an actuator construction which can accommodate limited flexure of the wing of the aircraft in use. A problem arises however where increased flexure of the wing occurs as this can result in jamming or fracture of components of the actuator.
U.S. Pat. No. 4,979,700 discloses an actuator construction in which flexure of the wing structure is accommodated by dividing the earth component bridging two adjacent slices in to two separate components, one for each slice, which can move relative to one another during wing flexure. It is believed that such a construction would accommodate a greater degree of wing flexure than that which can be accommodated by the actuator of European Patent 0174820 but the actuator disclosed in U.S. Pat. No. 4,979,700 has problems attendant upon the division of the earth component into two separate components. The construction disclosed in U.S. Pat. No. 4,979,700 requires the provision of an elongate central shaft extending along the longitudinal axis of the actuator, in order to prevent the slices of the actuator becoming separated before mounting of the actuator to the wing, and to assist in axial location of the slices when the actuator is in use. No significant torque load is transmitted through the shaft during use of the actuator but of course the shaft takes up significant space within the actuator, and contributes to the overall weight of the actuator. Furthermore, the provision of the central shaft necessitates the use of hollow sun gear shafts for each actuator slice thereby contributing to an increased overall diameter of the actuator. Still further, unless a further increase in diameter is to be accommodated the space available for the sun gears is limited and thus the material thickness of the sun gear assemblies is restricted with consequential restriction in the torque which can be transmitted by the sun gear assemblies. Ultimately the disadvantage of limiting the torque which can be transmitted by way of the sun gears can lead to the need for a longer actuator (having more slices) than would otherwise be required, or to the provision of an actuator of significantly increased overall diameter and weight.
It is a primary object of the present invention to provide an actuator in which significant wing flexure can be accommodated without the disadvantages of the construction disclosed in U.S. Pat. No. 4,979,700.